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Behavior of diffusion flame under various gravity level was experimentally investigated for better understanding of flame stability. Flame length and width were measured as the function of gravity scale. Also, how the gravity affects on the stability and blow off behavior of the flame were discussed. The gravity level was artificially controlled by using a spin tester in the gravity range from G=1 to G=15, where G=1 means the gravity on the earth. The laminar diffusion flames of methane and propane gas were made on the tip of the small vertical pipe where the vertical direction means an opposite direction of the artificial gravity.The results showed that the flame became unstable with an increase of gravity level. The flame length decreased and the blue flame length increased with an increase of gravity level for every fuel. These results are explained by the promotion of natural convection flow which was caused by an increase of buoyancy force. The flickering of flame and blow off were observed in a high gravity level. It was confirmed that the instability of a diffusion flame strongly depended on the gravity level.(2)燃料噴出ノズル内流れと火炎形態の関連 燃料の噴出レイノルズ数と火炎形態を比較した結果、通常重力場ではノズル内流れが乱流化すると火炎も乱流火炎に移行したが、過重力場ではノズル内流れが層流でも火炎が乱流化することが確認された。これは、ノズル内流れの状態だけでなく、自然対流が火炎形態に強く影響することを示している。(3)気流中での燃焼特性との比較 過重力場の燃焼では、火炎の形成に伴って自然対流が強くなり、火炎の安定性が悪化することが予備実験で判明している。このような安定性の悪化のメカニズムをより詳細に検討するために、気流中での火炎の安定性を調べ、過重力場の結果と比較検討した。その結果、気流速度の増大に伴う火炎形態や火炎長さの変化が重力場の大きさを増大させた場合と類似していることがわかった。